U.S. patent application number 12/717156 was filed with the patent office on 2010-09-23 for high-intensity discharge lamp and lighting device.
This patent application is currently assigned to OSRAM-MELCO TOSHIBA LIGHTING LTD.. Invention is credited to Hiroyuki OGATA, Kazuyoshi Okamura, Katsuya Otani.
Application Number | 20100237797 12/717156 |
Document ID | / |
Family ID | 42357566 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100237797 |
Kind Code |
A1 |
OGATA; Hiroyuki ; et
al. |
September 23, 2010 |
HIGH-INTENSITY DISCHARGE LAMP AND LIGHTING DEVICE
Abstract
A high-intensity discharge lamp including an arc tube provided
with a heat-resistant translucent discharge vessel forming a
discharge space, an electrode structure, a discharge medium charged
in the discharge vessel, the discharge medium being composed of a
light-emitting metal including mercury and a starting gas, a
support member electrically connected with the electrode structure
of the arc tube and holding the arc tube and an outer bulb having
the arc tube disposed therein along a tube axis and sealed with a
support member at an end portion thereof. The electrode structure
has an electrode shaft hermetically sealed at each of opposed end
portions of the discharge vessel and having a tip portion disposed
in the discharge vessel, a coiled electrode wound around the tip
portion of the electrode shaft disposed in the discharge vessel,
and a recessed portion or a protruding portion formed on the
electrode shaft spaced from the coiled electrode. A lighting device
with the high-intensity discharge lamp is also described.
Inventors: |
OGATA; Hiroyuki;
(Yokosuka-Shi, JP) ; Otani; Katsuya; (Yamato-Shi,
JP) ; Okamura; Kazuyoshi; (Yokohama-Shi, JP) |
Correspondence
Address: |
DLA PIPER LLP US
P. O. BOX 2758
RESTON
VA
20195
US
|
Assignee: |
OSRAM-MELCO TOSHIBA LIGHTING
LTD.
Yokosuka-Shi
JP
|
Family ID: |
42357566 |
Appl. No.: |
12/717156 |
Filed: |
March 4, 2010 |
Current U.S.
Class: |
315/291 ;
313/623 |
Current CPC
Class: |
H01J 61/0732
20130101 |
Class at
Publication: |
315/291 ;
313/623 |
International
Class: |
H01J 61/36 20060101
H01J061/36; H05B 41/36 20060101 H05B041/36 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2009 |
JP |
2009-068258 |
Claims
1. A high-intensity discharge lamp comprising an arc tube
including: a heat-resistant translucent discharge vessel forming a
discharge space; an electrode structure including an electrode
shaft hermetically sealed at each of opposed end portions of the
discharge vessel and having a tip portion disposed in the discharge
vessel, a coiled electrode wound around the tip portion of the
electrode shaft disposed in the discharge vessel, and a recessed
portion or a protruding portion formed on the electrode shaft
spaced from the coiled electrode; and a discharge medium charged in
the discharge vessel, the discharge medium being composed of a
light-emitting metal including mercury and a starting gas.
2. The high-intensity discharge lamp according to claim 1, further
comprising: a support member electrically connected with the
electrode structure of the arc tube and holding the arc tube; and
an outer bulb having the arc tube disposed therein along a tube
axis and sealed with a support member at an end portion
thereof.
3. The high-intensity discharge lamp according to claim 2, wherein
the recessed portion or the protruding portion formed on the
electrode shaft is formed by a coil wound around the electrode
shaft.
4. The high-intensity discharge lamp according to claim 2, wherein
the recessed portion or the protruding portion formed on the
electrode shaft is formed by partially varying an outer diameter of
the electrode shaft.
5. The high-intensity discharge lamp according to claim 4, wherein
the recessed portion or the protruding portion formed on the
electrode shaft is formed by connecting the electrode shaft with an
electrode shaft having a different outer diameter.
6. The high-intensity discharge lamp according to claim 1, wherein
the discharge vessel is made of ceramics material having a
substantially spherical swelling portion and a small-diameter
tubular portion formed integrally therewith at each of both ends of
the swelling portion, and the electrode structure is inserted into
the small-diameter tubular portion and hermetically sealed with a
heat-resistant sealant.
7. The high-intensity discharge lamp according to claim 6, wherein
a centering coil is wound around the electrode structure at a
portion disposed in the small-diameter tubular portion.
8. The high-intensity discharge lamp according to claim 6, further
comprising: a support member electrically connected with the
electrode structure of the arc tube and holding the arc tube; and
an outer bulb having the arc tube disposed therein along a tube
axis and sealed with a support member at an end portion
thereof.
9. The high-intensity discharge lamp according to claim 8, wherein
the recessed portion or the protruding portion formed on the
electrode shaft is formed by a coil wound around the electrode
shaft.
10. The high-intensity discharge lamp according to claim 8, wherein
the recessed portion or the protruding portion formed on the
electrode shaft is formed by partially varying an outer diameter of
the electrode shaft.
11. The high-intensity discharge lamp according to claim 10,
wherein the recessed portion or the protruding portion formed on
the electrode shaft is formed by connecting the electrode shaft
with an electrode shaft having a different outer diameter.
12. A lighting device comprising: a lighting device body; the
high-intensity discharge lamp according to any one of claims 3, 4,
9 and 10 provided in the lighting device body; and lighting circuit
means for turning on the high-intensity discharge lamp.
13. The lighting device according to claim 12, wherein the lighting
circuit means for turning on a lamp is attached with choke ballast.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 2009-068258
filed in Japan on Mar. 19, 2009; the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a high-intensity discharge
lamp in which at least a pair of electrodes are provided so as to
face each other in an arc tube having a heat-resistant translucent
discharge vessel and which is charged with a discharge medium
including mercury, and to a lighting device using the discharge
lamp.
[0004] 2. Description of the Related Art
[0005] A high-intensity discharge lamp, such as a metal halide
lamp, composed of an arc tube, which is sealed as a main component
in a translucent outer bulb or the like through a support member
constituting a power feeder. The arc tube is a heat-resistant
translucent vessel made of ceramics or silica glass having a
straight tube shape, an oblong shape or the like, in which a pair
of electrodes is opposed to each other, each electrode being
provided on a tip portion of a lead-in conductor in, un which The
vessel. The arc tube is charged with a discharge medium, for
example, mercury, halide of light-emitting metal and dilution
gas.
[0006] The high-intensity discharge lamp is turned on by being
connected with a choke type ballast using a wire-wound transformer
which has conventionally been known in luminaires, or an electronic
ballast using an inverter or the like which has recently been
developed. The electronic ballast provides high-pulse voltages and
thus achieves high startability as well as small and compact size
but is disadvantageously expensive. On the contrary, the choke type
ballast is inferior in electrical performance such as pulse
voltages to the electronic ballast described above but is of lower
price and has a longer lifetime than a lamp. Accordingly, the choke
type ballast is still frequently used.
[0007] In the case of a high-intensity discharge lamp to be turned
on with the choke type ballast, a relatively long period is
required to start up a low starting voltage type discharge lamp
which has been applied most widely. To shorten the starting period,
conventionally, the following techniques have been used, for
example: means of attaching a start assist electrode or an enhancer
for radiation of ultraviolet ray, means of facilitating generation
of glow discharge by charging a radioactive element and inducing
initial electrons and a technique of attaching a start assist
element such as a proximity conductor to facilitate a shift from
glow discharge to arc discharge.
[0008] In a high-intensity discharge lamp of this type, it is known
that a relatively long period is required for start-up until
obtaining prescribed light emission and electrical characteristics,
such as vaporization of a metallic substance for light emission or
for adjusting electrical characteristics of a lamp, which is
charged in an arc tube.
SUMMARY OF THE INVENTION
[0009] The inventors of the present invention discovered that after
various studies in an attempt of shortening a starting period of
the high-intensity discharge lamp, a possible cause of too long
starting period is due to an electrode structure and that
improvement in the electrode structure can improve startup
characteristics.
[0010] Specifically, in the case of the high-intensity discharge
lamp, a lamp is attached onto a socket in the vertical state,
referred to as a base-up state where a base is located upward or a
base-down state where a base is located downward, or in an inclined
state. In this case, mercury or metal halide charged in an arc tube
evaporates during high-temperature operation (turning-on) and
ionized by discharge energy for light emission and, after
turning-off with energization stopped, is placed into a charged
state at room temperature, that is, mercury remains in a liquid
state and metal halide remains in a solid state in the arc
tube.
[0011] FIGS. 8 and 9 illustrate X-ray observation results of
progress of mercury with time after turning-off of a lamp. FIG. 8
is a partial longitudinal front view illustrating essential parts
of an arc tube La of a conventional metal halide lamp having a
ceramic discharge vessel. FIGS. 9A to 9D are descriptive views
illustrating deposit states of mercury on an electrode structure of
an upper electrode of FIG. 8 with time after the lamp is turned
off. In FIG. 8, reference character B indicates a swelling portion
B1 forming a discharge space, and reference character B2 indicates
a tubular portion having both ends (FIG. 8 illustrates only one
end; however, the other end is structured in the same way. The same
is applicable in the description below.), each inner diameter of
which is smaller than that of the swelling portion B1.
[0012] The discharge vessel B is provided with an electrode
structure D (FIG. 9A) comprised of an electrode shaft D1 and an
electrode D2. The electrode shaft D1 is a rod element which is made
of tungsten (W) or niobium (Nb) and penetrates through the
small-diameter tubular portion B2 and which is hermetically sealed
on outer-end portion side (not illustrated) thereof through
heat-resistant airtight adhesive. The electrode D2 is formed in a
coil shape by closely-winding a tungsten (W) wire around a tip
portion of the other end disposed in the swelling portion B1 of the
electrode shaft D1 approximately 5 turns.
[0013] Reference character D3 in FIG. 9 indicates a coil formed by
a molybdenum (Mo) fine wire wound around the electrode shaft D1 and
is provided to ensure that the electrode shaft D1 passes through a
center of the small-diameter tubular portion B2. The discharge
vessel B is charged with a discharge medium including liquid
mercury H, a metal halide and a starting gas.
[0014] The arc tube La is installed on a power feeder, which
usually also serves as a power supply portion, sealed in an outer
bulb (not illustrated) formed by hard glass or the like and
electrically connected with a base joined to an outer bulb end
portion.
[0015] As described above, in the high-intensity discharge lamp
attached onto the socket in the base-up or base-down state within a
luminaire, the mercury and metal halide charged in the arc tube La
evaporate during a high-temperature operation (turning-on) under an
energization state and is ionized by discharge energy for light
emission. After turning-off when energy is stopped, the charged
mercury and metal halide are maintained at room temperature state.
For example, mercury remains in a liquid state and metal halide
remains in a solid in the arc tube La, respectively.
[0016] At this time, a portion whose temperature drops earliest in
the arc tube is the electrode shaft D1 portion constituting the
electrode structure D. The portion projects into and exposed to a
discharge space from the swelling portion B1 and the small-diameter
tubular portion B2 of the discharge vessel B and has a smallest
heat capacity. The vaporized one of the mercury H with high vapor
pressure is deposited on the electrode shaft D1 portion rapidly
cooled (FIG. 9B--4 minutes after turning-off) from one to another.
In the electrode structure D positioned on an upper side, the
mercury H deposited and cooled to be liquefied on the electrode
shaft D1 portion falls down the electrode shaft D1 portion by
gravitation resulting from an increasing number of liquefied
droplets and gathers on a top face of a stepped portion having a
large diameter formed by an end of the coiled electrode D2 (FIG.
9C--6 minutes after turning-off). When the liquefied mercury H
further increases, the mercury falls down by gravitation and covers
a surface of the coiled electrode D2 including a tip portion
thereof (FIG. 9D--8 minutes after turning-off). However,
particularly, mercury H having high surface tension maintains this
state until the next turning-on without falling down from the
coiled electrode D2 portion due to a low magnitude of vibration
even if the mercury is stored in a teardrop form.
[0017] Herein, it has been proven that when a tip portion of the
coiled electrode D2 which is a discharge trigger is covered with
the gathering mercury H, a part of energy required for discharge
start at lamp start-up runs short due to absorption in the mercury
H and a relatively long period is required for start-up. Further,
it has been proven that because a relatively long period is
required for start-up, sputtering of electrode material increases,
which causes degradation of characteristics such as lumen
maintenance factor of a lamp.
[0018] In the electrode structure D positioned on a lower side, as
described above, vapor of mercury H deposited on the electrode
shaft D1 after the lamp is turned off liquefies, falls down the
electrode shaft D1 by dead weight thereof and gathers on a root
portion (hermetically sealed portion, for example) of the electrode
shaft D1. Accordingly, the structure illustrated in FIG. 8 poses no
special problem; however a lamp in which an electrode shaft having
a main electrode such as a high-intensity mercury lamp and an
electrode shaft having an auxiliary electrode for start-up are
proximately in parallel, as described later, may cause no lighting
of a lamp due to falling-down mercury, which results from the
mercury gathering over between the root portions of both the
electrodes, thereby to short a lamp circuit.
[0019] It is an object of the present invention to provide a lamp
which is equipped with an electrode structure having a coiled
electrode on an electrode shaft and which is charged with a
discharge medium including mercury therein and in particular, a
high-intensity discharge lamp having high startability by
preventing mercury from adhering to a tip portion of the electrode,
and to provide a lighting device capable of facilitating start-up
of the high-intensity discharge lamp using an inexpensive
ballast.
[0020] According to a first aspect of the present invention, there
is provided a high-intensity discharge lamp including an arc tube
provided with: a heat-resistant translucent discharge vessel
forming a discharge space; an electrode structure including an
electrode shaft hermetically sealed at each of opposed end portions
of the discharge vessel and having a tip portion disposed in the
discharge vessel, a coiled electrode wound around the tip portion
of the electrode shaft disposed in the discharge vessel, and a
recessed portion or a protruding portion formed on the electrode
shaft spaced from the coiled electrode; and a discharge medium
charged in the discharge vessel, the discharge medium being
composed of a light-emitting metal including mercury and a starting
gas.
[0021] According to the first embodiment of a high-intensity
discharge lamp further comprising: a support member electrically
connected with the electrode structure of the arc tube and
retaining the arc tube; and an outer bulb having the arc tube
disposed therein along a tube axis and sealed with a support member
at an end portion thereof.
[0022] According to such an embodiment of the present invention, in
a high-intensity discharge lamp which is turned on in a vertical or
inclined state using a base-up or base-down structure, after the
lamp is turned off, mercury vaporized in an arc tube adheres to an
electrode shaft having the smallest heat capacity and cooled to be
liquefied. However, a flow of the liquefied mercury is stored by a
recessed portion or a protruding portion formed on the electrode
shaft, thereby to suppress liquefied mercury preventing a discharge
from adhering to a tip portion of the coiled electrode.
[0023] The present invention can be effectively applied to,
particularly, an embodiment of a high-intensity discharge lamp
using a small ceramic discharge vessel. That is to say, according
to an embodiment of the present invention, the discharge vessel,
made of ceramic material, is provided with a substantially
spherical swelling portion and small-diameter tubular portions on
both ends of the swelling portion formed integrally therewith. The
electrode structure is inserted into the small-diameter tubular
portion and hermetically sealed by a heat-resistant sealant.
[0024] In such a high-intensity discharge lamp, an inner diameter
of an opening for inserting the electrode structure, of an end
portion of the discharge vessel is small; therefore, a wire
diameter of the coil electrode wound around the electrode shaft
cannot be increased. Accordingly, by forming the recessed portion
or the protruding portion on the electrode shaft to store liquefied
mercury therein or thereon, the liquefied mercury which may block a
discharge can be inhibited from adhering to the tip portion of the
coiled electrode under a state where the inner diameter of the
opening of the tip portion of the discharge vessel remains small.
Thus, in addition to shortening the start time of the
high-intensity discharge lamp, sputtering of the electrode material
can be suppressed, thereby to suppress degradation of the lumen
maintenance factor.
[0025] In describing the present invention and the following
respective embodiments, unless otherwise specified, definitions of
terms and technical meanings are as described below.
[0026] As materials of the discharge vessel of the arc tube, the
following materials are available: sapphire, ceramics such as
aluminum oxide (alumina), oxide of yttrium-aluminum-garnet (YAG),
yttrium oxide (YOX) and aluminum nitride (AlN), highly
heat-resistant translucent material formed from hard glass such as
silica glass, orosilicate glass and aluminosilicate glass, or
highly corrosive-resistant material formed from halide.
[0027] The translucent material may be a light diffusion material
regardless of whether or not the material is transparent, provided
that the material has appropriate light transmission capability of
transmitting the light generated by a discharge and emitting the
light to the outside. The portion that hardly receives a radiation
by a discharge such as vessel end portion may use a light-shielding
material.
[0028] A shape of the longitudinal section 0f the discharge vessel
is oblong/elliptical, spherical, tubular, complex thereof or the
like and opening end portions facing each other are hermetically
sealed to form sealed portions. The sealed portion may be sealed
with a plug made of metal, ceramics, cermet or the like or sealant
such as heat-resistant sealant in use of ceramics, or may be sealed
by heat-melting the opening portion in use of silica glass or the
like.
[0029] In the case of a ceramic discharge vessel, the electrode is
constructed by connecting a plurality of members, for example, two
members in which an electrode shaft made of tungsten (w) or doped
tungsten provided with an electrode is directly welded in series,
or four members welded in series through an intermediate member
made of molybdenum (Mo) or cermet and the lead-in conductor between
the two members, with an outer conductor formed by a rod, a pipe or
the like also serving as a sealing member made of sealing metal
such as niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr),
hafnium (Hf) and vanadium (V).
[0030] In the case of a discharge vessel made of silica glass, a
foil material or a wire material of molybdenum (Mo) or tungsten (W)
is used as a sealing metal. By connecting the electrode shaft made
of the wire material of molybdenum (Mo) or tungsten (W), the inner
conductor and the outer conductor with the sealing metal, a
comb-shaped electrode is constituted.
[0031] A material of the electrode structure may be appropriately
selected according to a coefficient of thermal expansion of that of
each of a discharge vessel and sealant. The lead-in conductor made
of halogen-resistant material such as the molybdenum (Mo) or cermet
suppresses a difference between coefficients of thermal expansion
of the electrode member and the sealing metal as well as heat
transfer from the hot electrode portion to the sealed portion.
[0032] The discharge medium includes a light-emitting substance
such as mercury or a compound thereof, for example, metal halide
and amalgam. The metal halide may use any one type or a plurality
of types of the following known materials: for example, sodium
(Na), thallium (TI), indium (In), lithium (Li) and cesium (Cs) or
rare-earth metal such as dysprosium (Dy), holmium (Ho), thulium
(Tm), scandium (Sc), neodymium (Nd) and cerium (Ce) as
light-emitting metal and iodine (I), bromine (Br), chlorine (Cl)
and fluorine (F), according to light-emitting efficiency, light
emission characteristics such as color rendering properties and
light-emitting color, lamp power or an internal volume of a
discharge vessel.
[0033] In addition, as dilution gas, neon (Ne) or argon (Ar) is
sealed; however, other dilution gas may be sealed as needed. The
dilution gas is a starting gas and a buffering gas and is sealed in
the discharge vessel so as to provide a pressure of approximately 1
atmospheric pressure or higher.
[0034] As the outer bulb, A type, AP type, B type, BT type, ED
type, R type, T type and the like are available, which are made of
glass such as hard glass, for example, silica glass and orosilicate
glass and semihard glass or a translucent heat-resistant material.
A mount (support member) holding the arc tube is inserted from the
opening of the end portion and the opening is heated with a burner
to be directly melted and closed or a stem is used to form a sealed
portion. In the case of an outer bulb of T (straight tube) shape,
the sealed portion may be formed at both ends thereof. In addition,
the outer bulb inside may be in either of a vacuum atmosphere or an
inert gas atmosphere where dilution gas such as nitrogen (N2) or
argon (Ar) is sealed therein.
[0035] The support member has a portion sealed in the sealed
portion which requires a material having high hermetical properties
and fitness to the outer glass. Accordingly, it is appropriate to
constitute a feeder line portion in an outer tube, a sealing member
portion of the sealed portion, an external lead portion led out to
the outside of the outer tube and the like by connecting a
plurality of materials. It is sufficient if specifications such as
materials and dimensions are properly selected according to type,
electric power, weight, outer bulb material and the like.
[0036] The feeder line portion of the support member inside the
outer bulb, made of metal material such as molybdenum (Mo) or
tungsten (w), is electrically connected with the outer conductor at
both ends of the arc tube for power supply and for support member
for mounting and retaining the arc tube along a tube axis.
[0037] Further, there may be provided an intermediate tube
surrounding the arc tube, which is made of a heat-resistant
translucent material of substantially same ceramics, silica glass
or hard glass as the vessel; however, the intermediate tube is not
an essential member. The intermediate tube provides enhanced
light-emitting characteristics such as high efficiency and high
color rendering properties by enabling thermal insulation of the
arc tube and facilitating operation of the light-emitting metal as
well as protection against breakage of the arc tube.
[0038] According to an embodiment of the present invention, there
is provided a high-intensity discharge lamp including: a recessed
portion or the protruding portion formed on an electrode shaft, in
which the recessed portion or the protruding portion is formed by a
coil wound around the electrode shaft.
[0039] That is to say, by winding a coil around the electrode shaft
spaced from the coiled electrode of the tip portion, a protruding
portion to be formed by a coil wound the electrode shaft and a
protruding portion to be formed by no presence of a coil are formed
on the electrode shaft. The recessed portion can be used as a
mercury storage portion for storing mercury falling down the
electrode shaft after the lamp is turned off.
[0040] According to another embodiment of the present invention,
there is provided a high-intensity discharge lamp, in which the
recessed portion or the protruding portion on the electrode shaft
is formed by partially varying an outer diameter of the electrode
shaft.
[0041] That is to say, at the electrode shaft portion spaced from
the coiled electrode, there are provided either one or both of a
recessed portion having a smaller diameter than that of the
electrode shaft and a protruding portion having a larger diameter.
Further, by forming an inclined surface on the recessed portion or
the protruding portion, these portions are made to serve as a
mercury storage portion or a mercury fall-down portion. The
recessed portion and the protruding portion formed on the electrode
shaft can store liquefied mercury or can be made to fall down. The
recessed portion and the protruding portion may be formed
integrally with an electrode shaft or may be integrally formed by
joining members having different diameters from each other.
[0042] According to still other embodiment of the present
invention, there is provided a lighting device including: a
lighting device body, the high-intensity discharge lamp in either
one of the embodiments attached to the lighting device body and a
lighting circuit device for turning on the high-intensity discharge
lamp.
[0043] The lighting device (luminaire) according to the respective
embodiments can shorten a start-up period because of no deposition
of mercury to the tip portion of the coiled electrode of the
lamp.
[0044] The lighting device according to the present invention
includes, in a broad sense, all apparatuses/devices that use light
emission of the high-intensity discharge lamp for some purpose. For
example, the present invention is applicable to a compact
self-ballasted high-intensity discharge lamp, an ordinary
luminaire, a luminaire for facilities such as sports facilities,
public facilities and factories, a light source apparatus for
ceiling headlight optical fiber, an image projection apparatus, a
photochemical apparatus and others.
[0045] According to still other embodiment of the present
invention, a lighting device includes choke type ballast in a
lighting circuit for turning on a lamp.
[0046] The lighting device according to the respective embodiments
can shorten a start-up period under a turning-on state with choke
type ballast.
[0047] In the present invention, at least one pair of electrode
structures are provided; however, even only one of the pair of
electrode structures may be advantageously used. The size, the
number, volume and position of the recessed portion or the
protruding portion formed on the electrode shaft vary depending
upon rating, size and volume of the mercury sealed in the arc tube;
therefore studies such as previous tests are required. In addition,
the lamp may be turned on in an inclined, horizontal posture and in
any other postures with respect to the lamp axis.
[0048] Further, transverse or slanting cut groove may be formed on
the electrode shaft surface spaced from the coiled electrode or a
metal mesh may be wound so that the electrode shaft surface is
roughed for storage of a large amount of mercury thereon.
[0049] A high-intensity discharge lamp according to an embodiment
of the present invention can prevent mercury from adhering to a tip
portion of a coiled electrode, thus improving startability such as
shortening a start-up period. Discharge from mercury is inhibited;
therefore, deterioration, exhaustion and consumption of mercury can
be suppressed, thereby providing a high-intensity discharge lamp of
high quality, such as a metal halide lamp.
[0050] In addition, a lighting device according to another
embodiment of the present invention is provided with the
high-intensity discharge lamp according to the embodiment, thereby
providing a lighting device, such as a luminaire, excellent in
quality such as startability and light-emitting
characteristics.
[0051] Further, a lighting device (luminaire) according to another
embodiment of the present invention can shorten a start-up period
in a lighting device (luminaire) mounted with existing choke type
ballast.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1 is a front view of an outline structure of a
high-intensity discharge lamp according to an embodiment of the
present invention;
[0053] FIG. 2 is an enlarged longitudinal sectional view of an arc
tube portion in FIG. 1;
[0054] FIGS. 3A to 3D are enlarged front views of a tip portion of
an upper electrode structure in FIG. 2 and illustrate deposit
states of mercury on the electrode structure with time after the
lamp is turned off;
[0055] FIG. 4 is a longitudinal sectional view of an outline
structure of a lighting device (luminaire) for a high ceiling to
which the high-intensity discharge lamp illustrated in FIG. 1 is
attached;
[0056] FIGS. 5A to 5D are enlarged front views of an essential part
of an electrode structure according to another embodiment used for
a high-intensity discharge lamp of the present invention and
illustrate deposit states of mercury on the electrode structure
with time after the lamp is turned off;
[0057] FIGS. 6A to 6F are enlarged front views of essential parts
of electrode structures according to other embodiments used for a
high-intensity discharge lamp of the present invention;
[0058] FIG. 7 is a front view of an arc tube according to another
embodiment used for a high-intensity discharge lamp of the present
invention;
[0059] FIG. 8 is a longitudinal sectional view of a structure of an
essential part of a conventional arc tube; and
[0060] FIGS. 9A to 9D are enlarged front views of a tip portion of
an upper electrode structure in FIG. 8 and are descriptive views
illustrating deposit states of mercury on the electrode structure
with time after the lamp is turned off.
DETAILED DESCRIPTION
[0061] Embodiments of the present invention will be described in
detail with reference to the accompanying drawings. FIG. 1 is a
front view of an outline structure of a high-intensity discharge
lamp according to an embodiment of the present invention. FIG. 2 is
an enlarged longitudinal sectional view of an arc tube portion in
FIG. 1. FIGS. 3A to 3D are enlarged front views of a tip portion of
an upper electrode structure in FIG. 2 and illustrate deposit
states of mercury on the electrode structure with time after the
lamp is turned off.
[0062] A high-intensity discharge lamp L illustrated in FIG. 1
includes an arc tube 1A, a support member 5 supporting the arc tube
1A and constituting a power feeder, an outer bulb 6 housing the arc
tube 1A and the support member 5 therein and a base 7 joined to an
end portion of the outer bulb 6.
[0063] The arc tube 1A illustrated in FIG. 2 includes a discharge
vessel 2 and electrode structures 3a, 3b. The discharge vessel 2 is
made of ceramic material such as translucent alumina and
constructed by integrally forming a swelling portion 21
substantially spherical in a longitudinal sectional shape with
small-diameter tubular portions 22a, 22b joined by a curved surface
continuous to both ends of the swelling portion. The electrode
structures 3a, 3b are inserted into the small-diameter tubular
portions 22a, 22b of the discharge vessel 2 and hermetically sealed
with a heat-resistant sealant 23.
[0064] As illustrated in FIG. 2, each of the electrode structures
3a, 3b includes three members: an electrode shaft 31 made by a
tungsten (W) wire; a lead-in conductor 32 made by a molybdenum (Mo)
wire and constituting an intermediate member; and an outer
conductor 33 made by a niobium (Nb) wire and serving as a sealing
line. The three members are joined to each other in series by
appropriate means such as butt-welding. On a tip portion of the
electrode shaft 31, as illustrated in FIG. 3A, there are attached a
coiled electrode 30 formed by closely winding approximately 5 turns
(approximately 100% pitch) of a tungsten (W) fine wire and a coil
34 formed by closely winding approximately 2 turns of a tungsten
fine wire at a position above the coiled electrode 30 and spaced
from the coiled electrode 30 by approximately 4 turns. The lead-in
conductor 32 is provided with a coil 35 formed by closely winding
(approximately 100% pitch) a molybdenum (Mo) fine wire to ensure
that the electrode structures 3a, 3b are centered in the
small-diameter tubular portions 22a, 22b of the discharge vessel 2.
Here, the coiled electrode 30 closely wound around the tip portion
of the electrode shaft 31 and the coil 34 closely wound at a
position above thereof and spaced therefrom by approximately 4
turns form protruding portions protruding from a peripheral surface
of the electrode shaft 31, respectively and a relatively recessed
portion 41 is formed on the electrode shaft 31 between the coiled
electrode 30 and the coil 34.
[0065] As illustrated in FIG. 2, the electrode structures 3a, 3b
inserted into the small-diameter tubular portions 22a, 22b are
arranged so that the electrodes 30, 30 are opposed to each other at
a predetermined discharge interval in the swelling portion 21. The
outer conductors 33 of the electrode structures 3a, 3b are
hermetically sealed in the small-diameter tubular portions 22a, 22b
with the heat-resistant sealant 23.
[0066] In this case, a gap between each of inner faces of the
small-diameter tubular portions 22a, 22b and each of outer faces of
the lead-in conductors 32, around which the coils 35 are wound, is
set to be 0.1 mm or less (they may be in contact with each
other).
[0067] Starting and buffering gases including neon (Ne) and argon
(Ar), for example, as a discharge medium, metal halide as
light-emitting metal and mercury are charged in the discharge
vessel 2 of the arc tube 1A. The metal halide includes sodium
iodide (NaI), thallium iodide (TlI), indium iodide (InI) and
thulium iodide (TmI.sub.3), for example.
[0068] The outer bulb 6 is made of translucent hard glass such as
borosilicate glass. As illustrated in FIG. 1, the outer bulb 6 is
formed into a so-called BT type, which has a swelling portion 61 in
a center thereof and a small-diameter top portion 62 with its lower
end closed and a neck portion 63 on an upper side of FIG. 1. The
neck portion 63 has a sealed portion (not illustrated) where a stem
65 is sealed. An E-type base 7 is attached to cover the sealed
portion.
[0069] To a pair of internal lead-in wires 66, 67 extending from
the stem 65 sealed in the outer bulb 6, the support member 5 for
supporting the arc tube 1A is connected and fixed. That is to say,
one internal lead-in wire 66 of a wire material or a plate material
made of nickel, for example, is connected and fixed, by appropriate
means such as welding, to a proximal end portion side of a support
wire 51 formed into a substantially elongated U-shape, using the
wire material in the present embodiment.
[0070] In addition, a pair of metal support plates 52, 52, attached
so as to bridge the support wires 51 extending in parallel to each
other at a middle portion of the support wire 51, support the arc
tube 1A by pressing and holding the small-diameter tubular portions
22a, 22b, extending from both ends of the arc tube 1A, from the
outside.
[0071] Further, a middle tube 60, made of silica glass and having a
cylindrical shape with open upper and lower ends, for example, is
fixed to the support plates 52, 52 herein, being spaced by a
predetermined distance from the arc tube 1A. A reinforcing member
69 made of ceramics (such as alumina) is spirally wound around the
middle tube 60.
[0072] The outer conductor 33 led out of the lower small-diameter
tubular portion 22b of the arc tube 1A is electrically connected to
a metal conductor plate 53 attached so as to bridge the support
wires 51. On the other hand, the outer conductor 33 led out of the
upper small-diameter tubular portion 22a is electrically connected,
via a feeder line 55, with a conductor 54 connected to the other
internal lead-in wire 67.
[0073] With such a structure, supporting of the arc tube 1A and the
middle tube 60 is not complete. Accordingly, metal blade-like
elastic (spring) members 56, 56 in elastic contact with an inner
wall of the top portion 62 may be attached to a side surface in the
vicinity of a tip portion of the support wire 51 extending into the
small-diameter top portion 62 of the outer bulb 6. The elastic
(spring) members 56, 56 can support the arc tube 1A so as to be
positioned on a central axis of the outer bulb 6.
[0074] A start assisting circuit is connected in parallel to the
upper and lower electrodes 30, 30 in the arc tube 1A. The start
assisting circuit includes a glow starter for start-up 81, a
thermally-actuated switch 82 using a bimetal and a resistor 83.
[0075] Bridge members 57, 57 are made of an electrical insulating
material and bridge the support wire 51, the thermally-actuated
switch 82 and the resistor 83 for reinforcement thereof. The bridge
member 57 constitutes the support member 5 together with the
support wire 51, the support plates 52, 52, the conductor plate 53
and the elastic (spring) members 56, 56. In addition to the elastic
(spring) members 56, 56, an elastic (spring) member in elastic
contact with the inner wall of the small-diameter neck portion 63
may be attached to support the support wire 51.
[0076] The high-intensity discharge lamp illustrated in FIG. 1 is
attached to a lighting device (luminaire) 9 for illumination
illustrated in FIG. 4, for example, as a metal halide lamp L of a
double-tube structure which houses the arc tube 1A in the BT-type
outer bulb 6.
[0077] FIG. 4 is a longitudinal sectional view illustrating an
embodiment of the lighting device (luminaire) for a high ceiling to
which the high-intensity discharge lamp L is attached. In the
luminaire 9 illustrated in FIG. 4, a socket 92 is attached to a
support base 91 serving as a mounting portion to a ceiling surface
or the like. A guard 93 is provided around the socket 92. At a
lower end of the guard 93, there is fixed a conical reflecting
shade 94 which is made of a metal plate or enamel and has an inner
surface as a reflecting surface. When the base 7 of the discharge
lamp L is inserted in the socket 92, supporting of lamp and
electrical connection are achieved. Although not illustrated in the
present embodiment, alighting circuit device using choke ballast
and a power switch of the discharge lamp L are provided separately
from the luminaire body 91.
[0078] The lighting device (luminaire) 9 is attached to a ceiling
surface of sports facilities; for example, so that the support base
91 is attached to the ceiling surface with an opening side of the
reflecting shade 94 faces downward. The lighting device (luminaire)
9 is of a so-called base-up type, in which the discharge lamp L is
inserted in the socket 92 in a substantially vertical state with
the base 7 at the top. When a power switch (not illustrated) of the
lighting device (luminaire) 9 is turned on, the discharge lamp L is
energized by a power supply via the lighting circuit device and the
socket 92.
[0079] At starting up of the discharge lamp L, a voltage is applied
to both electrodes 30, 30 and both terminals of the glow starter 81
connected in parallel via a terminal of the base 7, through the
lead-in wires and the electrode structure 5. A discharge is
generated between discharge electrodes made of bimetal in the glow
starter 81 with low resistance, low impedance and the smallest
distance therebetween due to the voltage application, so that
ultraviolet rays are radiated, with which the electrodes 30, 30 in
the arc tube 1A are irradiated.
[0080] With the additional operation of this ultraviolet ray
radiation, electrons are released from surfaces of the both
electrodes 30, 30 and the initial number of electrons increases,
thus attaining increased discharge. Then, the bimetal in the glow
starter 81 comes in contact due to a thermal actuation resulting
from the discharge, thereby stopping the discharge. At the moment
the bimetal cools down due to the discharge stop and the electrodes
separate from each other, high-voltage pulses occur at the ballast
of the lighting circuit device, which are applied to the electrodes
30, 30. By the application of the high-voltage pulses, a discharge
is generated between the electrodes 30, 30 to start up the lamp L
and subsequently, a stable turning-on state is maintained.
[0081] After predetermined time of illumination, the discharge lamp
L is turned off by switching off the power switch (not illustrated)
of the lighting device (luminaire) 9.
[0082] In the discharge lamp L according to the embodiment of the
present invention, mercury H adheres to the upper electrode
structure 3a in the discharge vessel 2 with time after turning off
of the discharge lamp L by turning the power switch off. The
inventors of the present invention observed the mercury deposition
with an X-ray camera. As a result, mercury deposition states as
illustrated in FIGS. 3A to 3D were observed. Specifically, FIG. 3A
illustrates a mercury deposition state immediately after
turning-off. FIG. 3B illustrates a mercury deposition state
approximately four minutes after turning-off. FIG. 3C illustrates a
mercury deposition state approximately six minutes after
turning-off. And FIG. 3D illustrates a mercury deposition state
approximately eight minutes after turning-off.
[0083] Under a high-temperature atmosphere immediately after
turning-off, as illustrated in FIG. 3A, most of mercury having a
high vapor pressure is vaporized, so that deposition of liquid
mercury on the electrode shaft 31 or the like is not found.
Approximately four minutes after turning-off, as illustrated in
FIG. 3B, the vaporized mercury in contact with a surface of the
electrode shaft 31 having a small heat capacity is cooled down at a
portion having a smallest diameter of the electrode structure 3a
between the coil 34, in which is closely wound by approximately 2
turns and the coil 35, becomes liquefied mercury H and falls down
to a top face of an end portion of the coil 34 on a lower side.
[0084] Approximately 6 minutes after turning-off, as illustrated in
FIG. 3C, liquefied mercury H gathers in a teardrop form on the top
face of the end portion of the coil 34. At approximately 8 minutes
after turning-off, as illustrated in FIG. 3D, the vaporized mercury
is gradually cooled down on the electrode shaft 31, so that the
liquefied mercury increases in volume. The increased mercury
gathers on the top face of the end portion of the coil 34, and the
resulting overflowing liquefied mercury H falls down across a
surface of the coil 34 and flows into the recessed portion 41
between the coil 34 and the coiled electrode 30 with no coil
thereon. Thus, liquefied mercury H can be gathered in the recessed
portion 41 and the mercury H can be suppressed from adhering to a
tip portion of the electrode 30 forming a discharge trigger.
[0085] Specifically, in the high-intensity discharge lamp L using
the electrode structure 3a having the structure described above,
after turning-off of the lamp L that was turned on in a vertical
state, cooled-down and liquefied mercury H flows into and stored in
the recessed portion 41 formed on the electrode shaft 31 between
the coil 34 wound at a middle portion of the electrode shaft 31 and
the coiled electrode 30.
[0086] Accordingly, since the recessed portion 41 stores the
liquefied mercury H as a storage portion for liquefied mercury H,
deposition of the liquefied mercury H in a manner blocking
discharge at the tip portion of the electrode 30 can be suppressed.
Accordingly, at starting up of the lamp L, a discharge can be
generated from the material forming the electrode 30, and thus the
start-up time of the lamp L can be shortened. Because a discharge
is not blocked by mercury H, alteration or deterioration and
exhaustion of the electrode material can be suppressed, improving
the quality of the high-intensity discharge lamp L and the lighting
device (luminaire), such as stable discharge and longer life
time.
[0087] FIGS. 5A to 5D are enlarged front views of an essential part
of an electrode structure according to another embodiment used for
a high-intensity discharge lamp of the present invention and
illustrate deposition states of mercury on the electrode structure
with time after the lamp is turned off. FIGS. 5A to 5D illustrate
deposition states of mercury with the same amounts of time after
the lamp is turned off as FIGS. 3A to 3D, respectively and
therefore, the same components as in FIG. 3 are assigned the same
reference symbols and the description thereof is not repeated.
[0088] In an electrode structure 3c illustrated in FIGS. 5A to 5D,
as illustrated in FIG. 5A, a portion of the electrode shaft 31
which is lower than a portion having a wound coil 35 and is nearer
to the coiled electrode 30 is reduced in diameter, thereby forming
a recessed portion 42. As illustrated in FIG. 5B, the electrode
structure 3c, approximately minutes after turning-off, vaporized
mercury adheres to the electrode shaft 31 which has a smallest
diameter and a smallest heat capacity of the electrode structure 3c
and a surface in the vicinity of the recessed portion 42 and is
cooled down to become liquefied mercury H. Subsequently,
approximately 6 minutes after turning-off, the liquefied mercury H
illustrated in FIG. 5C falls down and flows into the recessed
portion 42 in a teardrop form.
[0089] Then, approximately 8 minutes after turning-off, as
illustrated in FIG. 5D, vaporized mercury gradually adheres to the
electrode shaft 31, so that liquefied mercury increases and mercury
H overflowing from the recessed portion 42 falls down to the top
face of the end of the coiled electrode 30. However, the flow of
mercury is blocked on the top face of the end of the coiled
electrode 30 of a large diameter protruding from a peripheral
surface of the electrode shaft 31, thereby gathering the mercury on
the top face of the end. Thus, the mercury H can be suppressed from
adhering to the tip portion of the electrode 30 forming a discharge
trigger.
[0090] The recessed portion 42 formed at a middle portion of the
electrode shaft 31 in the electrode structure 3c may be formed by
cutting the electrode shaft 31 to be reduced in diameter or
connecting a metal member of a smaller diameter to the middle
portion of the electrode shaft 31.
[0091] FIGS. 6A to 6F are enlarged front views of essential parts
of electrode structures according to other embodiments used for a
high-intensity discharge lamp of the present invention. In FIGS. 6A
to 6E, the same components as the electrode structure illustrated
in FIG. 3 or FIG. 5 are assigned the same reference symbols and the
description thereof is not repeated.
[0092] An electrode structure 3d illustrated in FIG. 6A has a
similar structure to the electrode structure 3c illustrated in FIG.
5 except for that the electrode shaft 31 is formed with a tapered
recessed portion 42'. Liquefied mercury smoothly falls down to the
tapered recessed portion 42' to be stored therein.
[0093] An electrode structure 3e illustrated in FIG. 6B has a
structure similar to the electrode structure 3d illustrated in FIG.
6A except for that a protruding portion 43 of an inverted conical
shape is formed below a tapered recessed portion 42' on the
electrode shaft 31. Liquefied mercury can be stored on a top face
of the protruding portion 43. In addition, a recessed portion 44 as
illustrated by broken lines may be formed on a top face side of the
inverted conical protruding portion 43, thus storing a larger
amount of liquefied mercury. Liquefied mercury overflowing from the
top face of the inverted conical protruding portion 43 is stored on
the top face of the coiled electrode 30.
[0094] An electrode structure 3f illustrated in FIG. 6C is formed
with recessed portions 45, 45 and protruding portions 46, 46
arranged alternately on the electrode shaft 31, thus storing a
larger amount of liquefied mercury in the plurality of recessed
portions 45, 45. The number of the recessed portions 45, 45 and the
protruding portions 46, 46 may be two or more, respectively.
[0095] An electrode structure 3g illustrated in FIG. 6D is formed
with a slit 47 in a longitudinal, transverse or slanting direction
on a peripheral surface of the electrode shaft 31 to increase a
surface area of the electrode shaft 31, thus storing a larger
amount of liquefied mercury.
[0096] In an electrode structure 3h illustrated in FIG. 6E, a metal
mesh 48 is wound around a surface of the electrode shaft 31 to
increase a surface area thereof, thus storing a larger amount of
liquefied mercury.
[0097] An electrode structure 3j illustrated in FIG. 6F has a
similar structure to that in FIG. 6B and the electrode shaft 31 is
formed with a conical protruding portion 49 having a larger
diameter than an outer diameter of the coiled electrode 30. The
mercury liquefied by being in contact with the electrode shaft 31
smoothly falls down along a top surface of a protruding portion 49
and drops outward of the electrode structure 3j without hitting the
electrode 30, thereby preventing mercury from remaining on the
electrode 30. In the electrode structure 3j, the electrode shaft 31
is formed into the same diameter and no tapered recessed portion is
formed.
[0098] As described above, the respective electrode structures 3c
to 3j illustrated in FIG. 5A and FIGS. 6A to 6F can suppress
liquefied mercury H from adhering to the coiled electrode 30
forming a discharge trigger after turning-off by forming recessed
portions 42', 44, 47, protruding portions 43, 46, 49 or a mesh 48
on the electrode shaft 31. Thus, each of the embodiments also
provides a high-intensity discharge lamp and a lighting device
(luminaire), capable of exhibiting the same operation and
advantageous effects as the embodiments illustrated in FIGS. 1 to
3.
[0099] The recessed portions formed on the electrode shaft 31 in
the above-described electrode structures 3a to 3h are formed to
serve as a storage portion for mercury. On the other hand, the
protruding portion in the electrode structure 3j illustrated in
FIG. 6F is formed to serve as a falling-down portion for mercury to
positively drop mercury along a conical inclined surface. The
recessed portions and the protruding portions may reversely serve
as the falling-down portions and the storage portions for mercury,
depending upon a direction along which the lamp is mounted. In
addition, the recessed portion and the protruding portion are
relative concepts and, for example, if a recessed portion is
formed, a protruding portion as well is inevitably generated.
[0100] FIG. 7 is a front view of an arc tube according to another
embodiment used for a high-intensity discharge lamp of the present
invention. In FIG. 7, the same components as in FIG. 2 are assigned
the same reference symbols and the description thereof is not
repeated. An electrode structure 3k used in an arc tube A2
according to the embodiment of the present invention includes an
electrode shaft 31 made of a tungsten (W) or molybdenum (Mo) wire
connected with one end of sealing metal 36 made of a molybdenum
(Mo) foil or the like and an external conductor 33 made of a
molybdenum (Mo) wire connected with the other end of the sealing
metal 36. The electrode shaft 31 as a main electrode has protruding
portions 46, 46 similar to those of the electrode structure
illustrated in FIG. 6C and a recessed portion 45 formed
therebetween.
[0101] On both ends of a straight silica glass tube constituting
the discharge vessel 2, upper and lower sealed portions 25a, 25b
are formed by thermally pressing end portions thereof. There are
provided a set of electrode structure 3k in the upper sealed
portion 25a. Another set of electrode structure 3k and a start
assisting electrode 30s are hermetically sealed in parallel to each
other in the lower sealed portion 25b, respectively. Mercury and
argon (Ar) are charged in the discharge vessel 2, which is further
sealed in the outer bulb to form a high-intensity mercury lamp (not
illustrated).
[0102] The high-intensity mercury lamp also provides improved
startability without adhesion of liquefied mercury to tip portions
of the coiled electrodes 30, after turning-off. In the lower
electrode structure 3k, liquefied mercury is stored in the recessed
portion and on the protruding portions 46, 46. An electrical short
due to gathering liquefied mercury between roots of the electrode
structure 3k and the assist electrode 30s is prevented, thereby
preventing generation of troubles such as no lighting-up. Specific
example of the present invention will be described below in
detail.
First Example
[0103] An arc tube 1A of a structure illustrated in FIG. 2 is
sealed in an outer bulb 6 of a lamp L illustrated in FIG. 1.
[0104] A discharge vessel 2, made of alumina, of the arc tube 1A is
approximately 20 mm in a maximum inner diameter and approximately
25 mm in an inner length at a central portion, and approximately
1.5 mm in an inner diameter and approximately 25 mm in an inner
length of each of small-diameter tubular portions 22a, 22b.
[0105] Each of the electrode structures 3a, 3b has substantially
the same structure as in FIG. 3 and the electrode shaft 31 made of
tungsten (W) wire is approximately 0.75 mm in an outer diameter and
approximately 7 mm in a length. On the tip portion of each
electrode shaft 31, there are provided a coiled electrode 30 around
which a tungsten (W) wire of approximately 0.3 mm in an outer
diameter is wound by 5 or 6 turns and a coil 34 around which the
wire is wound by approximately 2 turns, being spaced from the end
face of the coiled electrode 30 by approximately 0.5 mm.
[0106] A distance between the coiled electrodes 30, 30 opposed to
each other on the tip portions of the electrode structures 3a, 3b
is approximately 18 mm. A portion of the electrode shaft 31 between
the coiled electrode 30 and the coil 34 is approximately 0.5 mm in
a length and approximately 0.3 mm in a depth and a recessed portion
41 for storing mercury is formed at this portion.
[0107] In the discharge vessel 2, there is charged, as an ionizable
charged material, argon (Ar) gas of approximately 100 torr, mercury
of approximately 50 mg and approximately 10 mg of
NaI--TlI--TmI.sub.3--InI of 50:15:25:10 in a weight ratio.
Second Example
[0108] A lamp according to the second example is a ceramic metal
halide lamp having the same rating and structure as the first
example but has an electrode structure having the same structure as
in FIG. 5. Specifically, the recessed portion 42 formed on the
electrode shaft 31 (outer diameter: approximately 0.75 mm) in the
vicinity of the coiled electrode 30 in the electrode structure is
approximately 1.5 mm in an axial length and approximately 0.55 mm
in an outer diameter (depth: approximately 0.1 mm).
[0109] The inventors of the present invention fabricated ceramic
metal halide lamps according to the first and second examples and a
ceramic metal halide lamp of the same rating and structure as those
of the first example except for the electrode structure for
comparative use, and examined characteristics thereof, such as
startability. The lamp for comparative use has an electrode
structure D having the conventional structure illustrated in FIGS.
8 and 9.
[0110] Table 1 shows measurement results of the lamps having the
three types of electrode structures (4 lamps for each type), which
were obtained by reducing a power voltage of a mercury lamp with a
rated power voltage of 200 V to 180 V using choke ballast of 300 W
and measuring each start period (time (second) required to start an
arc discharge after a glow discharge).
[0111] For measurement of the start-up time, each lamp was turned
off after over 20 minutes' illumination and was left at room
temperature for over 4 hours.
[0112] As shown in Table 1, a lamp equipped with the electrode
structure having a recessed portion and a protruding portion on an
electrode shaft has achieved a good result of a shorter start-up
period by a few seconds than a lamp equipped with the conventional
electrode structure.
TABLE-US-00001 TABLE 1 LAMP TYPE [FIGURE OF FIRST SECOND
CONVENTIONAL ELECTRODE EXAMPLE EXAMPLE EXAMPLE STRUCTURE] [FIG. 3]
[FIG. 5] [FIG. 9] NO. 1 7.0 SECONDS 4.4 SECONDS 8.4 SECONDS NO. 2
6.9 SECONDS 6.8 SECONDS 7.8 SECONDS NO. 3 5.9 SECONDS 6.0 SECONDS
8.0 SECONDS NO. 4 6.5 SECONDS 4.7 SECONDS 10.7 SECONDS AVERAGE 6.6
SECONDS 5.5 SECONDS 8.7 SECONDS
[0113] Table 2 shows remeasurement results of start periods of the
same lamps under the same conditions. From the table,
reproducibility was verified with the same tendency as in Table
1.
TABLE-US-00002 TABLE 2 LAMP TYPE [FIGURE OF FIRST SECOND
CONVENTIONAL ELECTRODE EXAMPLE EXAMPLE EXAMPLE STRUCTURE] [FIG. 3]
[FIG. 5] [FIG. 9] NO. 1 7.6 SECONDS 4.0 SECONDS 9.2 SECONDS NO. 2
6.4 SECONDS 5.5 SECONDS 8.2 SECONDS NO. 3 4.6 SECONDS 4.6 SECONDS
6.4 SECONDS NO. 4 7.1 SECONDS 4.4 SECONDS 9.7 SECONDS AVERAGE 6.4
SECONDS 4.6 SECONDS 8.4 SECONDS
[0114] Table 3 shows measurement results of lumen maintenance
factors of the same lamps under the same conditions. Specifically,
the lumen maintenance factors in Table 3 were obtained by turning
on the lamps for 3,000 hours and 6,000 hours each in on-off cycles
of 6 hours in total, each cycle including turning-on period of 5.5
hours and turning-off period of 0.5 hours, and measuring the
resulting luminous flux degradation.
TABLE-US-00003 TABLE 3 LAMP TYPE [FIGURE OF FIRST SECOND
CONVENTIONAL ELECTRODE EXAMPLE EXAMPLE EXAMPLE STRUCTURE] [FIG. 3]
[FIG. 5] [FIG. 9] 3,000 HRS 67% 68% 62% 6,000 HRS 58% 60% 50%
[0115] The measurement results indicate that the lumen maintenance
factors of the high-intensity discharge lamps of the first and
second examples have been improved by 5 to 6 points for 3,000 hours
and 8 to 10 points for 6,000 hours than those in the high-intensity
discharge lamp of the conventional example. This may be because in
the high-intensity discharge lamps according to the first and the
second examples, liquefied mercury does not adhere to a tip portion
of an electrode shaft, which reduces sputtering of an electrode
material in starting a discharge, thereby to improve the lumen
maintenance factor.
[0116] The present invention is not limited to the embodiments
described above and various modifications and applications are
possible. For example, the high-intensity discharge lamp is also
applicable to other types of discharge lamps, without being limited
to metal halide lamps and mercury lamps and provides a
substantially same operation and advantageous effects as the
embodiments above.
[0117] In addition, the lighting device (luminaire) is also
applicable to other structures and applications without being
limited to the embodiments above. Further, the discharge lamp is
also applicable where the installation direction of the discharge
lamp is a slanting direction as well without being limited to
perpendicular installation such as base-up or base-down
installation
* * * * *